Remove unused OperatingSystem plugin.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@180993 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the initialization/termination of the now-removed OperatingSystemDarwinKernel.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@180994 91177308-0d34-0410-b5e6-96231b3b80d8